1. Field of the Invention
The present invention is concerned with a novel composition of matter—a designer, cyclic peptide that modulates the structure and function of the HIV main envelope protein gp120. The invention is related to the fields of medicinal chemistry, biochemistry and virology.
2. Description of Related Art
HIV-1—the virus responsible for the AIDS pandemic, infects the host's cells by means of receptor-assisted endocytosis. The viral glycoprotein gp120 and the cell's CD4 protein are implicated in the initial stage of attachment of the virus to the cell (Kwong et al. 1998). Following this initial attachment, gp120 undergoes a major conformational rearrangement (Myszka et al. 2000), exposing the chemokine co-receptor binding site and triggering subsequent stages of the fusion process, (Wyatt and Sodroski, 1998).
Haim et al., 2009, have shown that the inhibition of HIV-1 virus by the soluble form of CD4 (sCD4) and its certain less active, small molecule mimics, occurs due to premature triggering of the conformational change in gp120. The activated state of gp120, primed for binding to the co-receptor, is transient and its life span is measured in minutes. Afterward, it undergoes a further, irreversible conformational change, leading to a loss of binding competency. The induction of the activated conformation of gp120 by soluble CD4 mimics (SCMs) causes a moderate increase of the CD4-independent HIV infectivity at certain SCM concentrations range. At higher concentrations, the inhibitory effect is predominant. The possibility to trigger premature, spontaneous and irreversible deactivation of the viral protein responsible for the infectivity, by targeting the highly conserved region of this protein, is an elegant and attractive paradigm for the development of anti-HIV therapeutics, especially considering the independence of such drugs on the co-receptor tropism of particular HIV strains.
In addition to their role as antiviral drugs, SCMs have the potential to be used as immunostimulants, either amplifying the natural immune response, or the response induced by anti-HIV vaccines. This potential results from the observations that CD4-independent strains of HIV have an increased susceptibility to neutralizing antibodies (Kolchinsky et al. 1999, Kolchinsky et al. 2001, Thomas et al. 2003). This independency is caused by the exposure of the normally hidden epitopes that are responsible for co-receptor binding. Both sCD4 and SCMs cause precisely this effect: they trigger the conformational change of gp120 and expose the CD4-induced epitopes. Thus, in addition to being classical entry inhibitors, SCMs are expected to increase the susceptibility of the virus to the immune response of the infected organism.
Before the above-described mechanism of gp120 inhibition by sCD4 and SCMs has been recognized, it was speculated that the inhibition may occur due to competitive binding or via triggering the shedding of gp120, but regardless of the mechanism, efforts were undertaken to develop gp120-modulating molecules. While no SCMs currently are on the market, several compounds are at different stages of development. Relevant references include: include: Zhao et al. 2005, Stricher et al. 2008, Lin et al. 2003.
While the general purpose to controlling HIV infections, and the chemical nature of the compounds disclosed in the present invention makes them related to retrocyclins (Cole et al. 2002), it should be noted that retrocyclins are CD4 antagonists, whereas the compounds that the present patent application is concerned with, are, by their design, gp120 antagonists.